1. Field of the Invention
This invention generally relates to guidewires and catheters used in medical procedures and more specifically to a convertible wire that can operate either as a guidewire or as a catheter.
2. Description of Related Art
Medical guidewires are devices that can be navigated through narrow passages in the body. A physician controls the position and travel of a distal end of the guidewire by manipulations performed at a proximal end outside the body. Medical catheters generally comprise hollow, flexible tubes that convey fluids, such as contrast agents, embolic agents or pharmacological agents to or from a desired body vessel within the body. Guidewires and catheters sometimes have similar structures, so the term "wire" is often used to identify these devices in a generic sense. Some "wires", called "convertible wires" are adapted for use both as catheters and guidewires.
Physicians often use guidewires and catheters in combination. For example, a physician can position the tip of a guidewire at a site using its steering capability. Then the physician slides a catheter over the guidewire to the site. The physician removes the guidewire through the catheter and administers a fluid before removing the catheter.
These and other applications of guidewires and catheters in medical environments have led to several desirable, but , often antithetical, characteristics. For example, a convertible wire should have a small outer diameter to facilitate its transfer through the body with minimal trauma. However, if the outer diameter is too small, the resulting inner diameter, or lumen, limits the size of steering wires that can be accommodated in guidewire applications. In catheter applications, an unnecessarily small lumen can limit flow rates through it or the viscosity of fluids that can be accommodated by the wire. This, in turn, can limit the range of fluids administered through the catheter.
Convertible wires should be as flexible as possible so the guidewire or catheter moves easily through body passages. This can be achieved by using structures with thin walls. Yet the structure must be sufficiently strong to be safe in use, as can be achieved either by using thicker walls or internal safety wires. Such strength can dominate design criteria for catheters because fluid pressures encountered in catheters, particularly at the proximal end, can be in the order of hundreds of pounds per square inch.
The following disclose guidewires and catheters that achieve some of the foregoing desirable characteristics.
3,749,086 (1973) Kline et al PA1 4,003,369 (1977) Heilman et al PA1 4,719,924 (1988) Crittenden et al PA1 4,779,128 (1988) Machek PA1 4,798,598 (1989) Bonello et al PA1 4,846,186 (1989) Box et al PA1 U.S. application Ser. No. 07/276,106 filed Nov. 23, 1988 by Fernando Alvarez de Toledo for Small Diameter Guidewires of Multi-Filar Cross-Wound Coils, now U.S. Pat. No. 5,065,769 issued Nov. 19, 1991 which in turn is a continuation-in-part of Ser. No. 710514 filed Mar. 21, 1988 and issued as U.S. Pat. No. 4,932,419 on Jun. 12, 1990 titled Multi-filar, Cross-Wound Coil for Medical Devices.
Article Sos et al, A New Open-ended Guidewire/Catheter,
154 Radiology 817-818 (1985)
Kline et al d a spring guide that has closures at both ends, an elongated helically wound spring body and a composite internal core that facilitate flexing of a distal tip portion. The distal portion is made relatively more flexible than the proximal portion by a second spring that is coiled counter to that of a spring body. A plastic sheath covers the spring body.
Heilman et al disclose a guidewire that has a wound spring body formed of rectangular wire coated with Teflon.RTM.material prior to winding to provide an ultra-smooth surface. Alternatively the finished guidewire surface is electropolished. Special materials processing and tapering of an internal safety wire in the distal tip portion enhance distal tip portion flexibility.
Crittenden et al disclose a steerable guidewire with a solid elongated main wire or core. This core extends through a central passage defined by elongated outer and inner helical springs.
Machek discloses a catheter with a wound outer casing, an internal core wire and a safety wire. The wound outer casing has the form of a coil spring produced by winding Teflon.RTM.-coated rectangular wire. The core wire enables physicians to insert and twist the core wire relative to the casing thereby to steer the guidewire. The safety wire provides a backup should the steering wire break. The steering and safety wires, of course, require space within the guidewire and can limit the size and range of motions of any device to be inserted through the opening.
Bonello et al disclose a catheter guide with a closed-end distal tip portion formed by a coil spring. A proximal portion connects to a control mechanism and includes a coil wire. An outer plastic coating, deposited in a gaseous phase onto the spring, seals the tube and makes it smooth. The distal tip portion has no covering and adjacent coils in the spring are spaced to improve flexibility and to facilitate the exit of fluids from the catheter at the distal tip portion.
Box et al disclose a guidewire with a flexible wire core that extends through a proximal portion to a distal region where the core is characterized by tapered subregions internally of a flexible coiled wire spring. The wound spring has portions with adjacent coils touching; elsewhere adjacent coils are spaced to enhance flexibility.
Sos et al disclose an open-ended convertible wire that can operate as a guidewire or a catheter. The convertible wire consists of a wound spring guide with a Teflon sheath applied over a proximal portion. A distal tip is beveled and polished like that of a conventional catheter. It has been found, however, that for given outer diameter this structure limits the size of steering wires that can be used in guidewire applications. During use as a catheter for the administration of fluids, a physician must exercise care not to over pressurize the catheter.
Alvarez de Toledo discloses a small diameter wire with a multifilar coil and a polyimide sheath overlying the proximal portion. In an application as a guidewire the distal tip portion has a closed end and includes an extension of the coils and an inner coil. A core extends through the central passage formed by the springs in the inner and outer coils. In an application as a catheter, the structure comprises a spring body and a polyimide sheath extends over the length of the wire for strength.
While each of the foregoing references discloses a structure that provides one or more particularly desirable characteristic, none of them provide all the previously described desirable characteristics. For example, Kline et al and Heilman et al, Bonello and Box disclose structures that operate only as spring guides. Sos discloses a structure that can serve as a guidewire and a catheter, but it has a lumen that is smaller than desired. Further the maximum pressure limit for the wire in catheter applications is less than pressures encountered in many catheter applications. The Alvarez de Toledo reference discloses a basic structure that can be adapted to serve as a guidewire or a catheter but the specific guidewire and catheter implementations are different structurally. Moreover, neither structure shown by Sos et al or Alvarez de Toledo facilitates the insertion of the distal tip portion through body passages, although Sos et al polish a distal portion of a convertible wire. None of the references discloses a soft floppy a traumatic tip that operates in a guidewire or catheter application without detracting from the steering and fluid administration capabilities of the wire.